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INTRODUCTION As such, from an industrial hygienist's point of view, the historical recognition of the etiological aspect of CTS is scattered over many different sources spanning many decades. I have attempted here to coalesce the information concerning the historical etiological recognition, evaluation and control of CTS. I have limited my review to literature which appeared in English, primarily in the U.S., U.K. and Northern Europe. Industrial hygiene is the science and art devoted to the recognition, evaluation, anticipation and control of human stressors in the environment and in the work place which may cause sickness, impaired health, or significant discomfort among workers or among general members of the community. As an industrial hygienist, I have prepared this discussion with other industrial hygienists in mind. The human stressors can be manifest as chemical, radiological, physical or biological. The industrial hygienist is an individual who by formal training or experience has obtained knowledge of the effects of stressors on the human and is capable of recognizing when those stressors may become hazards and is capable of controlling stressors as hazards. Integral in the recognition of hazards which effect the biomechanics of the human body is a working knowledge of functional anatomy and ergonomic principals. Ergonomics is a field of industrial hygiene which is concerned about ensuring a proper fit between a human and the task they are involved in performing. Ergonomics, as a field, was created in 1949 and is a conjunction of the Greek "ergos" (to work) and "nomos" (surroundings). Although the word ergonomics is less than a century old, some ergonomic principals are prehistoric. ANATOMICAL BACKGROUND Where the tendon must travel over a curved path or over a bone, an area of increased friction is created. To protect the contacting surfaces during movement at these areas of high friction, the tendon is often invaginated in a protective sac called a bursa. Bursæ are lined with a synovial membrane and filled with fluid which helps to lubricate the sliding tendon. Occasionally, as a result of trauma, excessive use or disease, the bursæ or the synovial membrane may become inflamed and tender. Collectively, the inflammation of the bursa or synovial membrane is commonly termed bursitis and tenosynovitis, respectively. There are many other common terms used to describe the inflammation of the tendon.1 Throughout the body, and particularly where tendons must follow a curved path, ligamentateous structures form fibrous conduits which act as tunnels to constrain the tendons and their associated bursæ. These tunnels are typically not very pliable, and when the bursæ or synovial membranes are inflamed within the tunnel structure, the resulting swelling can reduce the volume of the area in which the tendon is invaginated. This reduction in volume can result in pain and tenderness when the tendon attempts to slide along its path. Additionally, if there are nerves or arteries which also occupy the tunnel, these structures too may become crowded, and their functional capabilities may be impaired. There are about 33 tunnels throughout the body in which entrapment due to inflammation is seen. The wrist and the elbow are two of the most common areas of tunnel entrapment. When the wrist is flexed (drooped forward), the tendons would have a tendency to "bow-string" across the front of the wrist. To keep the tendons in place along the curved path, the tendons (and other structures) are constrained in a particular tunnel in the wrist; the carpal tunnel. There are actually several other tunnels in the wrist, but those tunnels are beyond the scope of this discussion. When the hand is viewed palm-side-up (supinated), the roof of the tunnel is formed by two fibrous structures (proximal and distal) which are collectively given the name transverse carpal ligament (Figure 1 below shows the sectioned ligament, revealing the tendons and median nerve beneath). The transverse carpal ligament has several other common names, including flexor retinaculum, which is the term mostly used in this discussion.
Although there is considerable material on entrapment of the median nerve, much of the information concerns exclusively the physiology, occupational aspect or other limited view of the condition commonly called carpal tunnel syndrome (CTS).
Throughout the body, tendons transmit to bones and joints the contractive motion of muscles. Often, the tendons act as ropes around pulleys (called trochlea), and must freely slide along their path for maximal efficacy.
Sectioned Ligament
In the wrist, several structures must pass through a particularly small cross sectional area of the tunnel. Of these structures, the ones of particular concern are the median nerve; the four tendons of the flexor digitorum profundus; the four tendons of the flexor digitorum sublimis, and the flexor pollicis longus (Figure 3).
When the hand is supinated, the four sublimis tendons ride atop of the four profundus tendons. Collectively these tendons are invaginated in a "U"-shaped bursa called the ulnar bursa. Riding atop the ulnar bursa, sandwiched in between the bursa and the ligamentateous roof of the tunnel, is the median nerve.
Any inflammation within the tunnel will tend to decrease the available volume and squeeze those structures in the tunnel. Of paramount importance when such a reduction in volume occurs is the pressure which is placed on the median nerve.
When the median nerve becomes entrapped within the carpal tunnel due to a reduction in functional volume, several distinguishing symptoms can arise. A collection of numerous signs and symptoms is referred to as a "syndrome"; and when all of the right symptoms are present which indicate median nerve entrapment in the carpal tunnel, the resulting condition is referred to as "carpal tunnel syndrome" (CTS). 3
The median nerve (and its branches) provide both sensory and motor innervation to the hand. Impairment of the median nerve can result in sensory loss and muscle atrophy, leading to impaired health and significant discomfort to the worker. Therefore, the recognition, evaluation and control of occupational carpal tunnel syndrome lies squarely within the realm of the professional industrial hygienist.
HISTORICAL RECOGNITION
Several other names have been used to describe the syndrome over the years. Many of these names, (such as "tailor's neuritis" adopted by Edinger (1909) and "professional neuritis" adopted by Oppenheim et al (1914), 5were derived based on the observation that specific occupations appeared to be more prone to the complaint. Although the term CTS was not commonly in use until about the 1950's the syndrome and its occupational association were clearly recognized as early as 1909. Brouwer, 6in 1920, made the statement that hyperfunction of the hand muscles can be regarded as a cause of the symptoms which became known as CTS; and notes that several of his subjects are tailors.
Cited by Rosenbaum (1993), 7Walshe commented in 1945 on seeing an increased number of cases of acroparæsthesiæ in women during World War II and concluded that the increase was a result of the increased manual labor of the women during wartime.
Brain et al (1947), 8also noted a consistent occupational association between symptoms and occupation, and made the definitive leap to the conclusion that symptoms consistent with CTS are occupationally related by stating:
Some authors who write on the occupational association of CTS often quote G.S. Phalen, M.D., a prolific author who almost single handedly stood against the opinion of his published colleagues by stating in 1965 at the Annual Meeting of the American Society for Surgery of the Hand, New York:9
Phalen's statement makes the assumption that all cases of common, typical CTS are spontaneous CTS, i.e the etiology of the condition is not known. His statement is not correct because a significant number of the common cases of CTS are not spontaneous; the etiology is known to be occupationally related; yet Phalen apparently assumed that all cases of CTS which did not fit neatly into other pathologies must have been idiopathic.
It has been long recognized that overuse of the hands can result in tenosynovitis. It is possible that Phalen's assertions were clouded by an issue of semantics. Consider that Phalen concluded his 1956 paper with (the emphasis is mine):
Dr. Phalen's views were not generally accepted by his colleagues, and even Dr. Phalen himself recognized the association between occupation and CTS as early as 1950 when he presented a paper to the 99th Annual Session of the American Medical Association. 11 In that paper, Phalen discussed some of his patients and noted that symptoms were aggravated by any active use of the hands such as typing excessively and noted that one of his patients was a stenographer. Further, Phalen stated that:
Phalen concluded at the 99th Annual Session of the AMA that CTS was not occupationally related but rather occurred spontaneously. In response to this conclusion, Dr. Clarance Luckey
12 openly challenged Dr. Phalen by stating:
Phalen seems to have misinterpreted his own findings. In 1956 for example,13 he seemed to have overlooked one of his own very significant observations. At the 105th annual meeting of the American Medical Association, he stated:
This statement speaks to the issue of an observational flaw: If one does not recognize repetitive motion induced chronic tenosynovitis; then such a synovitis brought on by excessive repetitive motion will appear as spontaneous. Yet throughout Phalen's 1956 paper, he makes constant reference to that fact that excessive use of the hands aggravated the symptoms of CTS.
Other authors, however, were more willing to recognize the association between CTS and occupation. Kremer et al,14 for example, in 1953 recognized housework as an occupation, and noted that the precipitating factors for CTS attacks were knitting, sewing, wringing, washing, or writing. Kremer et al concluded that:
Heathfield (1957), 15noted that carrying of heavy baskets made the symptoms of CTS worse and that: "...the commonest aggravating causes were knitting and sewing."
Heathfield concludes:
In 1958, Liscomb 16
recognized inflammation of the tendon's vaginal sheath as being a causative factor in the development of CTS. He stated in his paper that:
And in his particular cohort, he notes that in all but three of the 29 subjects, "...the carpal tunnel syndrome was due definitely to tenosynovitis."
Liscomb was in agreement with most of his colleagues and today's industrial hygienists when he stated that:
The "irritative phenomena" which Dr. Liscomb alludes to is a thickening of the tendon sheath. Dr. Liscomb concluded in 1958, that occupational factors "probably" played a role in the production of tenosynovitis.
In 1959, Tanzer et al 17notes that occupations that involve wrist flexion is more significant than occupations which involve wrist extension in the production of CTS. They note that Love 18 identified three occupations which he thought might have contributed to the production of CTS, namely "very busy secretarial work, milking of cows by hand, and tailoring".
Tanzer concludes:
By 1960, CTS was becoming more established and better understood. In 1960, Dr. Crow, M.R.C.P. wrote in the British Medical Journal:19
According to Dr. Crow's paper, by 1960, diagnosis of CTS was "...commonplace in general medical, neurological and orthopædic practice." In Dr. Crow's study cohort, the onset of CTS was related (in varying degrees) to occupational factors, specific incidents, or strenuous use of the hands in 35 out of 81 subjects.
By 1966, the medical field was treating occupational CTS as old hat. Hymovich and Lindholm (1966) 20 stated in the Journal of Occupational Medicine:
In 1966, Phalen still was associating occupation with the onset of symptoms without recognizing a causal factor. For example, he stated that:21
Paradoxically, Phalen continued to recognize the temporal relationship between work and symptoms without accepting occupational causality:22
Other authors23 have also shown a temporal relationship between overtime hours worked and the number of treated CTS cases per year.
Some of the writings of Phalen are inconsistent. For example, Phalen stated24 that:
Within the same article, Phalen asserts:
And in another article:25
"It is obvious that resting the hands or a change of occupation is indicated for the patient who has had a recent onset of symptoms after an unusual amount of manual labor."
The ability of Phalen to simultaneously recognize and not recognize the strong and consistent association between certain occupational activities and the onset of CTS is puzzling.
Occupations at risk of CTS, were not as rare as Phalen suggested. In 1984, the U.S. Government listed the following occupations which were associated with CTS:26
In 1972, Phalen again authored a paper, 27 and although he still steadfastly rejected an occupational relationship and the onset of CTS, his position became even more ambiguous:
"Thickening of the flexor synovialis may be caused by prolonged, forceful grasping movements, and carpal tunnel syndrome may result. Under these conditions, carpal tunnel syndrome could be classified as an occupational disease, but this is an exceedingly rare cause of median nerve compression."
This statement by Phalen again was in conflict with his colleagues. In 1975, Birkbeck et al,28 published a study in which they looked at 658 patients with CTS. 79% of those patients were employed in industry which required highly repetitive light movements of the kind which have been shown to illicit tenosynovitis. In the study, the authors argued that changes in the nerve are a result of the repetitive movement of the fingers due to inflammation of the tenosynovial membrane.
The authors conclude that:
By the end of the 1970's, other medical researchers were openly arguing against Phalen's minority (but prolific) views with regard to the etiology of CTS. In 1978, Rothfleisch and Sherman 29 published a paper in which they stated that CTS as an occupational disease had not been adequately emphasized. The authors concluded that:
This view was shared by other researchers in the field of occupational health, such as Bernard 30 who in 1979 stated:
Nurse Bernard concludes that:
By the early 1980's the occurrence of occupationally related CTS was so well defined, that empirical models were in place to predict the risk associated with occupation. More detailed discussion of these models appears below.
One of the most significant findings which was beginning to surface was the strong association between the onset of CTS and vibrating hand tools (Cannon 1981).31,32
Cannon et al were not alone in recognizing the effects of vibration on the median nerve; Chatterjee et al 33 also noted that vibration had a debilitating effect on the median nerve and Koskimies et al, 34 specifically studied vibration as an etiologic factor in the CTS and concluded that:
In a study cited by Koskimies et al, 35 Ahlborg et al concluded that heavy manual work increased the risk of CTS by a factor of two; when combined with hand/arm vibration, the risk rose by a factor of five. Exceptionally heavy work with simultaneous exposure to vibration could increase the risk of contracting CTS by a factor of ten.
In 1985, the National Institute for Occupational Safety and Health (NIOSH) reported 36 that between 15% and 20% of workers employed in construction, food preparation, clerical work, mining and production fabrication were at risk of repetitive motion syndromes.
From around the early 1980's fewer and fewer investigators seriously disputed the occupational etiology of CTS. The direction of publications concerning CTS turned from "what is it?" to "how do we evaluate it?"
EVALUATION
In the pre-industrial-revolution society, occupations as trades were highly skilled practices of a kenisiologically complex nature. A farmer, fisherman or cobbler for example, spent their workday performing constantly changing activities. The cobbler for example may spend a little time cutting the shoe leather, a little time spinning the cord, some time at the last hammering in soles and so on. A trade was an ability to perform all of the needed tasks to manufacture the final product for market.
In the post-industrial-revolution society, on the other hand, things were becoming much different. The concept of the production line was becoming a reality; compartmental specialization was the key to corporate success. To increase the production of shoes, the manufacturer did not hire several master cobblers and expect them to work independently. Instead, the manufacturer would hire unskilled laborers to work at the production line. A worker need not know how to manufacture a whole shoe, now a worker need only know how to hammer on a sole, and be willing to do nothing but hammer on soles all day long.
As the century progressed, the workforce became involved in performing minute repetitive tasks for lengthy periods of time. Any minor stress that the old-time cobbler may have endured while hammering on a sole would soon be relieved during some other step in the process. Any stress related to the hammering of a sole for the production worker, would be magnified since there was no break in the manual activity which was needed to spread small stresses out over the course of the day.
The result is that as production line manufacturing became more popular, the occurrence of repetitive motion syndromes became more prevalent. Some occupations inherently have repetitive motions both in the pre and post industrial revolution worlds. An example of such an occupation is tailoring. It is for this reason, that certain occupations were already associated with the onset of repetitive motion syndromes such as CTS.
Injurious stress to the hands comes primarily from two sources:37 1) excessive use against resistance, and
2) use while in an abnormal position.
As mentioned earlier, the flexor tendons of the hand follow a curved path as the wrist is flexed. During flexion and extension of the wrist, the contact force on the ulnar bursa and the median nerve is increased. 38
The tendons may be thought of as belts wrapped around pulleys (trochlea formed by the flexor retinaculum and the osseo-aponeurotic canals) which lift loads (the fingers). This analogy is suitable for several reasons. First it helps to explain a puzzle put forth by Phalen and others: Why do woman suffer from CTS more than men? Phalen incorrectly stated 41 that there was no structural differences between the carpal tunnels of men and women. More precisely, he should have stated that there are no anatomical differences between the carpal canals of the two sexes. As a physician, he looked only at the number of tendons, their respective locations and so forth. Based on this criteria, there are no structural differences. However, from an industrial hygienist's point of view, the anatomist has over looked the obvious: a woman's hand is generally smaller. From an ergonomical and kinesiological / biomechanical aspect, the smaller wrist size is very significant.
The force exerted on a pulley (FL) is a function of four parameters. One of the parameters (the coefficient of friction between the pulley and the belt (µ) has been estimated experimentally 42 is not significant in the physiological model. The significant parameters are given below.
The term "carpal tunnel syndrome" was in common use as early as 1953 when Kremer et al 4discussed similarities between CTS and other syndromes which appeared to have similar or identical symptoms to CTS. In 1953, Kremer et al noted, in particular, that the syndrome referred to as "acroparæsthesiæ" (adopted by Schultze, in 1893 to denote the nocturnal burning in the fingers of individuals) may in fact have been CTS.
"There can be little doubt that occupation is a causal factor. [of median nerve compression in the carpal canal]"
"The common, typical, carpal-tunnel syndrome- spontaneous compression neuropathy of the median nerve in the carpal tunnel-is not an occupational disease"
"We believe that spontaneous compression neuropathy of the median nerve in the carpal tunnel is not an occupational disease."
This may be the crux of Phalen's apparent lack of recognition of a strong and consistent association between certain occupational activities and the onset of CTS. For no one would argue that spontaneous compression of the median nerve is occupationally related, but conversely, occupationally related CTS is not spontaneous. This view is supported by Kremer et al, 10 who in 1953 recognized that spontaneous and occupational CTS differed only in recognized origin."Our view is in accord with that first put forward by McArdle (1951), that the focal point in production of the [CTS] syndrome is the median nerve as it passes through the carpal tunnel. In those patients in whom the site of the lesion was known to be the wrist, the clinical syndrome was indistinguishable from that which occurs spontaneously."
"Any condition which might increase the volume of the structures contained within the carpal tunnel would tend to compress the median nerve beneath the volar carpal ligament [flexor retinaculum]. A chronic tenosynovitis of the flexor tendons of the fingers would represent such a condition."
"Dr. Phalen stated that these cases come on spontaneously. I think that you have to consider, in the differential diagnosis, that some of them are definitely of industrial origin."
"We are concerned, however, in this report with a spontaneous gradual compression neuropathy of the median nerve, without any evidence or history of injury or disease. We believe this condition in most instances results from a chronic, nonspecific synovitis involving the flexor synovialis [ulnar bursa] in the carpal tunnel."
"There is no doubt that sustained use of the hands during the day, for knitting, washing, or writing often causes an exacerbation of nocturnal [CTS] symptoms."
"Occupation,... [and other pathological and physiological conditions]... are of particular importance in ætiology."
"Only in the last few years has this syndrome [CTS] been recognized in the vast majority of instances as being due primarily to tenosynovitis."
"If the annular ligament [flexor retinaculum] is pressed against the tendon by hard objects, such as the handles of scissors, pruning shears or other tools, repeated movements of the fingers or the thumbs may cause the onset of irritative phenomena."
"A study of the occupations in twenty-two cases of carpal tunnel syndrome involving thirty-four hands suggests that repeated, forceful flexion of the wrist and fingers is frequently a precipitating factor."
"Thus, this syndrome [CTS] can be a source of great distress and disability to those affected by it."
"It has been long known that repetitive motion of the hand can cause injury, especially when some sort of tool or instrument must be held in the grasp."
"...the more severe symptoms [of CTS]...may have developed quite recently, often associated with a sudden change to a more strenuous manual labor."
"Strenuous use of the hands almost always aggravates the symptoms, although the increased numbness and tingling in the fingers may not be noted until the hand has been resting for several hours after the activity."
"If this syndrome of median neuropathy were to be due to occupational trauma alone, the condition certainly should be encountered much more commonly than it evidently has been."
"Such a condition does occur much more frequently than one might suspect. The apparent rarity of the syndrome is due to the physician's failure to consider this condition when making the differential diagnosis of pain and numbness in the thumb, index or middle fingers."
"Occupations that require active finger flexion with the wrist flexed should certainly predispose to a carpal tunnel syndrome, but fortunately such occupations are not common."
Typing Textile workers Postal workers Packing Musicians Haymaking Waitresses Metal fabricating Fruit packing Housekeeping Meat processing Upholstering Tire and rubber workers Gardeners Aircraft assembly Fabric cutting and sewing Automobile assembly Electronic assembly Buffing Inspecting Coking "I am certain that fibrosis or thickening of the flexor synovialis [ulnar bursa] within the carpal tunnel is the most common cause of carpal tunnel syndrome."
"Occupations, whether work or hobbies, involving light but highly repetitive movements of the fingers and wrists are likely to produce these changes."
"...under some conditions the CTS should be considered to be an occupational disease. These conditions appear to be fulfilled most readily by work or hobbies involving light, highly repetitive movement of the fingers and wrists."
"...Vibration and position [of the hand and wrist] are etiologic factors in the development of carpal tunnel syndrome in industrial workers."
"In terms of an occupational etiology, strong and repeated dorsiflexion of the wrist either singly or in combination with ulnar deviation, radial deviation, palmar flexion, and/or forearm movement is conducive to the development of carpal tunnel syndrome."
"Carpal tunnel syndrome exists, is a significant occupational health problem, and when looked for, is more common in industry than ordinarily thought to be."
"Heavy, repetitive work with exposure to hand/arm vibration increases the risk of carpal tunnel syndrome (CTS)."
As time progressed through the late 1800's and into the earlier years of this century, industrial hygiene saw an increased incidence of CTS. Was the increase due to more physicians becoming aware of the condition, or was there a reason which reflected the change in the occupational situation in the industrial world?
The tension on the tendon, (Ft)
The radius of the trochlea curvature, (r)
And the included angle of tendon-trochlea contact, (theta)
The force per arc length on the pulley is approximated by: 43
What we see is that the tendon load is approximately evenly distributed over the trochlea. The contact force between a tendon and trochlea increases as a function of tendon tension (load) and is inversely proportional to the radius of trochlea curvature. It has been long recognized that flexion and extension of the wrist increases the pressure on the median nerve.45-50 One astute author, 51 noted that ulnar angulation of the wrist is more pronounced in women than in men and suggested that this decreased radius may be a factor in another tunnel syndrome of the hand (de Quervain's disease).
Armstrong et al, 52 showed that for equal loads, the contact force on the female wrist was 25% greater than the male wrist during extension and 14% greater than the male wrist during flexion. I believe that along with other (primarily hormonal and other physiological / physiochemical characteristics) sexual differences, the smaller wrist curvature accounts for the greater incidence of "spontaneous" and occupational CTS in women than in men. As a result, in industry, a job function may be safe for one sex but unsafe for another.53
In order to properly evaluate the impact of a hazard, the industrial hygienist must have a working grasp of the concept of cause. In 1612, Galileo Galilei published his Discourse, in which he laid down his definition of "cause:" 54
"That which, given, the effect is there; and, removed, the effect is taken away."
Although simple, the definition lacks precision. In the definition 55 of "cause" that I accept as concise and reasonable, four criteria must be met. There should be a strong and consistent association between the event (the injury) and the insult (the activity); there should be a temporal relationship between the cause and the effect; there should be a physiologically plausible mode of action; and there should be a dose/response relationship.
Earlier in this discussion, I established the generally accepted recognition of a strong and consistent association between the onset of CTS and certain manual activities. I have established a temporal relationship 56 between manual activity and the onset of CTS symptoms, and I have established a biologically plausible explanation for the mechanisms involved.
What has been difficult to establish is a dose/response relationship. Unlike a toxicologist's "dose" which is a unit weight of substance administered per unit body weight per unit time, no such simple units are available for measuring the "dose" of the exposure to the factors which precipitate the onset of CTS. Some authors, 57 have attempted to better define dose by developing experimental designs which measure wrist angle, speed, force, body posture, acceleration and several other aspects of hand/arm movement. But to-date, the concept of dose with regard to the complexity of hand and wrist motion remains elusive.
Furthermore, by definition, CTS is a syndrome; thus, it is not a single response, but rather a constellation of various responses. Therefore, precise evaluation of the hazard must be expressed in terms of risk of contracting the syndrome based on secondary measurable factors.
By the middle 1970's the U.S. industry was sufficiently aware of CTS to begin large scale evaluations of the workforce. Following one such extensive evaluation, 58 a model was proposed which could be used to predict the risk of occurrence of CTS. Although the proposed model contains several uncertainties, it is a useful method for helping the industrial hygienist determine high risk occupations and high risk individuals employed in those occupations.
The following is excerpted from the evaluation 59 which describes the model.
"Continuity-corrected chi-square statistics were used to determine the differences between subjects and controls on age, race, sex, history of diabetes, presence of hypertension, type of gynecological surgery performed, body weight and occupational status.
Student's t-test was used to compare continuous variables among subjects and controls. The odds-ratio statistic was employed to determine the odds in favor of disease when specific predictors such as race, diabetic history or gynecological surgery were present. The logistic regression program BMDPLR was used to determine association between selected independent variables and the disease."
The cohort for the evaluation consisted of about 20,000 personnel. From the evaluation, four significant predictive variables were identified: 1) use of vibrating hand-tools, 2) history of gynecological surgery, 3) duration of employment, and 4) performance of repetitive motion tasks of the wrist.
Other industries and health professional were also evaluating the U.S. workforce.60-70
CONTROL
In the case of CTS, it seems that radical medical intervention (sectioning of the flexor retinaculum), has achieved favor over engineering controls (redesigning the work place).
Nonetheless, from the 1950's, publications cited in this discussion, 71,72
Between 1976 and 1984, NIOSH received 20 requests from industry for Health Hazard Evaluations involving 735 reported cases of CTS.73
The control of hazards in the industrial setting traditionally has followed a hierarchy of preferability:
Engineering controlsAdministrative controlsPersonal protection devicesMedical interventionMedical prophylactics
One of the medical intervention controls commonly prescribed as early as 1960, was the use of splints.75 Ironically, splints are still used today; and in many cases, the use of splints may only help to prolong the problem by attempting to fit the human to the task instead of fitting the task to the human.
In the middle 1960's, some physicians however, recognized that by attacking the root of the problem, the need for treatment could be avoided. In 1966, Dr. Hymovich stated:76
"It was apparent however, as with all diseases of occupational origin, that prevention of these [wrist] injuries would be even more efficacious in reducing their toll."
And to this end, Dr. Hymovich implemented a CTS prevention program at his factory (The Bunker-Ramo Corporation). The controls employed by Hymovich in 1966 were the same types of controls which are recommended today.
The model control program should begin by analyzing the hand movements of the injured workers to determine if other methods of performing the same job could be developed and implemented. The following correctable parameters all contribute to the precipitation of CTS.
Hand Movement Against Resistance
Vibration Transmission From a Hand Tool Into the Hand
In some limited cases, gloves can be used to reduce the vibration from the tool. Depending on the frequency of vibration, the gloves may or may not provide effective protection. 88,89
The weight of the tool should be as evenly distributed such that the center of gravity of the tool approximates the center of grip (point of grip). Where the tool is excessively heavy and/or unbalanced (awkward), grasp points such as extended and adjustable handles should be incorporated (or retrofitted) on the tool.
The linear grip span (the widest distance between the handle of the tool and the trigger or activator) should be consistent with standard anthropomorphic principles.
It was known as early as 1974 91
Awkward Positioning of the Hand When Using a Tool
Tichauer (1966) explained how tools themselves could be the insulting occupational factor. Tools which were symmetrical, but which needed to be grasped and rotated orthoaxially, forced the wrist into sharp ulnar deviation. This motion, particularly when combined with a flexed wrist, was shown to increase the pressure on the median nerve. It was shown that the axis of rotation of a hand tool should be aligned with the true limb axis of rotation, not with the anatomical axis of rotation.
The work piece should be positioned with respect to the employee, such that the wrist is maintained in a neutral (natural-relaxed) position. The height of the work piece should be such that the wrist is straight when the elbow is held at a 90° angle and the back is maintained in a straight (neutral "S" shaped vertical) position.
Repetitive Movement of the Hand and Fingers
An administrative control would be to rotate the employee's jobs such that they perform different motions, thus preventing the trauma associated with repetition.
The employees should be instructed in the nature of repetitive motion disorders and instructed on how to avoid them. Enhanced supervision should be provided by trained supervisors to ensure that the trained employees continued to use the prescribed practices.
Poorly Designed Hand Tools
By 1967, 99Hand movement against resistance.77Vibration transmission from a hand tool into the hand. 78 Prolonged excessive gripping of a tool. 179Awkward positioning of the hand when using a tool. 80,81Repetitive movement of the hand and fingers. 82Poorly designed hand tools. 83
By addressing each of these, the risk of CTS can be reduced or eliminated.
Where possible, a substitution of powered tools for hand tools should be sought; particularly for those jobs which require significant repeated pronation and/or supination of the hand. Powered hand tools should not impose a torque on the users hand of any greater than 12 inch-pounds. 84
Segmented vibrational energy has been shown to increase the incidence of CTS 85particularly when the vibration is in the frequency range of 10 to 40 hertz.86 To control the vibration, several design features can be incorporated such as increasing the mass of the tool. (However, increasing the mass of the tool can have detrimental effects if the employee must wield the tool for lengthy periods of time.) Another technique would be to incorporate vibration absorption devices such as absorption collars which inhibit the transmission of the vibration to the hand. Around 1962, 87
Prolonged Excessive Gripping of a Tool
Engineering controls which use counter balanced spring suspensions to make heavier tools easier to handle should be designed and built. The weight of a hand tool should be a balance between sufficient mass to absorb the vibration, but not excessive to increase unnecessary grip and sufficiently low weight if the tool is to be used extended in front of the body.
Dr. Tichauer (1966) was early on the scene with complex discussions 92 concerning the use of advanced ergonomic principles to reduce injuries. Those 1966 discussions are as pertinent now as they were then. It was shown that tools and body posture could be a major factor in increasing physiological cost of performing work.
Where repetitive movements cannot be avoided, appropriate work/rest cycles should be implemented to give the hands a rest. Also, where repetitive movements cannot be avoided, exaggerated flexion and/or extension of the wrist should be avoided by redesigning the layout of the work area such that the wrist and arm are maintained in the neutral position discussed above.
Since the 1940's, 93 it was recognized that an improperly designed tool could result in injury to the median nerve. Some physicians 95 simply removed the offending tool from the workplace.
In addition to the design criteria mentioned above, in the middle 1960's it was recognized that form-fitting tools could increase worker discomfort and could result in injuries. 96,97
Medical Surveillance
Non-invasive medical tests such as electromyography, Wormster's, Tinel's and Phalen's tests could be used for early detection of CTS. Upon the recommendations of a physician, the employee (and the employer) could be advised of the condition and assigned new duties.
SUMMARY AND CONCLUSION
With the exception of a single prolific author, the occupational etiology of CTS was accepted and well established by the medical profession and the industrial hygiene profession as early as the 1960's. Industry, industrial hygiene and medical professionals recognized what conditions precipitated CTS and methods for the control of those conditions were in use by the end of the 1960's and early 1970's.
Any employer in the 1960's who was concerned about the CTS phenomena had several resources through which an evaluation could be made; The American Industrial Hygiene Association and NIOSH are but two such organizations in the U.S. that made information available.
I believe that the resistance of some insurance companies, physicians and managers to accept CTS as a condition which can be caused by workplace exposures is unreasonable in light of the preponderance of evidence in peer reviewed journals.
As a special note, I would like to make the observation that many of the so-called "ergonomic devices" (wrist-rests, mouse pads, etc) that I have seen contradict good industrial hygiene ergonomics. Most of the wrist-rests we have seen on the open market are more likely to create wrist problems rather than solve wrist discomfort. At this point, I would recommend against purchasing any "ergonomic" products until the work area has been evaluated by a competent industrial hygienist, physician or health practitioner with demonstrated experience in the fields of kinesiology and ergonomics. Following the ergonomic evaluation, in the event that the work area cannot be re-designed to fit the worker, an ergonomic device may be recommended.
(With the caveat that in our area, some people who use crystals and Voodoo have taken to calling themselves "kinesiologists." Kinesiology is the study of the principals of mechanics and anatomy in relation to human movement. Kinesiology does not involve herbs, spices, aroma therapy, soft music or "crystal power.")
References are found at the bottom of the page.
A very special word of thanks to Randale Sechrest, MD who was kind enough to allow me to use the exceptionally fine graphics found in this discussion. Additional information can be found at Medical Multimedia Group, 308 Louisiana Avenue, Libby, Montana 59923
2 Robbins H. Anatomical study of the median nerve in the carpal tunnel and etiologies of the carpal tunnel syndrome. Journal of Bone and Joint Surgery 1963; 45A: 953.
3 Langloh N, Linscheid R. Recurrent and unrelieved carpal-tunnel syndrome. Clinical Orthopædics and Related Research 1972; 83: 41-47.
4 Kremer M, Gilliatt RW, Golding JSR et al. Acroparæsthesiæ in the carpal-tunnel syndrome. Lancet 1953: 590-595.
5 Brouwer B. The significance of phylogenetic and onto-genetic studies for the neuropathologist. The Journal of Nervous and Mental Disease 1920; 51(2): 113-136.
6 Ibid
7 Rosenbaum RB, Ochoa JL, Carpal Tunnel Syndrome and Other Disorders of the Median Nerve Butterworth-Heinemann, 1993 p.32.
8 Brain RW, Wright DA, Wilkinson M. Spontaneous compression of both median nerves in the carpal tunnel. Lancet 1947:277-282.
9 Phalen GS. The carpal-tunnel syndrome: 17 years experience in diagnosis and treatment of 654 hands. The Journal of Bone and Joint Surgery 1966; 48A: 211-228.
10 Kremer M, Gilliatt RW, Golding JSR et al. Acroparæsthesiæ in the carpal-tunnel syndrome. Lancet 1953: 590-595.
11 Phalen G.S. Spontaneous compression of the median nerve at the wrist. Journal of American Medical Association 1951; 45: 1128-1133.
12 Ibid
13 Phalen GS, Kendrick JI. Compression neuropathy of the median nerve in the carpal tunnel. Journal of American Medical Association 1956; 64: 524-530.
14 Brouwer B. The significance of phylogenetic and onto-genetic studies for the neuropathologist. The Journal of Nervous and Mental Disease 1920; 51(2): 113-136.
15 Phalen GS, Kendrick JI. Compression neuropathy of the median nerve in the carpal tunnel. Journal of American Medical Association 1956; 64: 524-530.
16 Lipscomb PR. Tenosynovitis of the hand and the wrist: carpal tunnel syndrome, de Quervain's disease, trigger digit. Clinical Orthopedics 1958; 13: 164-181.
17 Tanzer RC. The carpal tunnel syndrome. A clinical and anatomical study. The Journal of Bone and Joint Surgery 1959; 41A(4): 626-634.
18 Love JG. Median Neuritis; carpal tunnel syndrome; diagnosis and treatment. North Carolina Medical Journal 1955;16: 463-469.
19 Crow RS. Treatment of the carpal-tunnel syndrome. British Medical Journal 1960: 1611-1615.
20 Hymovich L, Lindholm M. Hand, wrist and forearm injuries: the result of repetitive motions. Journal of Occupational Medicine 1966; 8(11): 573-577.
21 Phalen GS. The carpal-tunnel syndrome: 17 years experience in diagnosis and treatment of 654 hands. The Journal of Bone and Joint Surgery 1966; 48A: 211-228.
22 Ibid.
23 Masear VR, Hayes JM, Hyde AG. An industrial cause of carpal tunnel syndrome. The Journal of Hand Surgery 1986; 11A(2): 222-227.
24 Phalen G.S. Spontaneous compression of the median nerve at the wrist. Journal of American Medical Association 1951; 45: 1128-1133.
25 Phalen GS. The carpal-tunnel syndrome: 17 years experience in diagnosis and treatment of 654 hands. The Journal of Bone and Joint Surgery 1966; 48A: 211-228.
26 Preventing Illness and Injury in the Workplace, Washing DC: U.S. Congress, Office of Technology Assessment, OTA-H-256, April 1985.
27 Phalen GS. The carpal tunnel syndrome. Clinical Evaluation of 598 Hands Clinical Orthopædics and Related Research 1972; 83: 29-40.
28 Birbeck MQ, Beer TC. Occupation in relation to the carpal tunnel syndrome. Rheumatology and Rehabilitation 1975; 14: 218-221.
29 Rothfleisch S, Sherman D. Carpal tunnel syndrome: biomechanical aspects of occupational occurrence and implications regarding surgical management. Orthopædic Review 1978; 7: 107-109.
30 Bernard ML. Carpal tunnel syndrome: identification and control. Occupational Health Nursing 1979: 5-17.
31 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
32 Feldman RG, Goldman R, Keyserling MW. Peripheral nerve entrapment syndromes and ergonomic factors. American Journal of Industrial Medicine 1983; 4: 661-681.
33 Chatterjee, DS, Barwick DD, Petrie A, Exploratory electromyography in the study of vibration-induced white finger in the rock drillers. British Journal of Industrial Medicine 1981, 39: 89-97.
34 Koskimies K, Färkkilä M, Pykkö I. et al. Carpal tunnel syndrome in vibration disease. British Journal of Industrial Medicine 1990: 411-416.
35 Ahlborg G, Voog L. Vibration exposure and distal compression of the median nerve ("carpal tunnel syndrome"). Läkartidning 1982; 79: 4905-4908.
36 Preventing Illness and Injury in the Workplace, Washing DC: U.S. Congress, Office of Technology Assessment, OTA-H-256, April 1985.
37 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
38 Armstrong T, Chaffin DB. Some biomechanical aspects of the carpal tunnel. Journal of Biomechanics 1978: 567-570.
39 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
40 Lipscomb PR. Tenosynovitis of the hand and the wrist: carpal tunnel syndrome, de Quervain's disease, trigger digit. Clinical Orthopedics 1958; 13: 164-181.
41 Phalen G.S. Spontaneous compression of the median nerve at the wrist. Journal of American Medical Association 1951; 45: 1128-1133.
42 Armstrong T, Chaffin DB. Some biomechanical aspects of the carpal tunnel. Journal of Biomechanics 1978: 567-570.
43 Armstrong T, Chaffin DB. Some biomechanical aspects of the carpal tunnel. Journal of Biomechanics 1978: 567-570.
44 Ibid.
45 Ibid.
46 Brain RW, Wright DA, Wilkinson M. Spontaneous compression of both median nerves in the carpal tunnel. Lancet 1947: 277-282.
47 Phalen G.S. Spontaneous compression of the median nerve at the wrist. Journal of American Medical Association 1951; 45: 1128-1133.
48 Nissen KI. Etiology of carpal tunnel compression of the median nerve: in proceedings of the joint meeting of the orthopædic associations of the English-speaking world. Journal of Bone and Joint Surgery 1952; 34B: 514-515.
49 Phalen GS, Kendrick JI. Compression neuropathy of the median nerve in the carpal tunnel. Journal of American Medical Association 1956; 64: 524-530.
50 Tanzer RC. The carpal tunnel syndrome. A clinical and anatomical study. The Journal of Bone and Joint Surgery 1959; 41A(4): 626-634.
51 Bunnell, Sterlin: Surgery of the Hand, ed 3, Philadelphia, Ippincott, 1956.
52 Armstrong T, Chaffin DB. Some biomechanical aspects of the carpal tunnel. Journal of Biomechanics 1978: 567-570.
53 Tichauer ER, Sc.D. Ergonomics: the state of the art. American Industrial Hygiene Association Journal 1967: 105-116.
54 Drake, Stillman: CAUSE A Galilean Dialogue Incorporating a New English Translation of Galileo's Experiment "Bodies That Stay atop Water, or Move In It" and Science. University of Chicago Press, Chicago. 1981.
55 Brand P, (Editor) Recent Results in Cancer Research, Occupational Cancer Epidemiology, 1990 Vol120, page 6.
56 Phalen GS, Kendrick JI. Compression neuropathy of the median nerve in the carpal tunnel. Journal of American Medical Association 1956; 64: 524-530.
57 Schoenmarklin RW, Marras WS. Effects of handle angle and work orientation on hammering: I. wrist motion and hammering performance. Human Factors 1989; 31(4): 397-411.
58 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
59 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
60 Koskimies K, Färkkilä M, Pykkö I. et al. Carpal tunnel syndrome in vibration disease. British Journal of Industrial Medicine 1990: 411-416.
61 Schoenmarklin RW, Marras WS. Effects of handle angle and work orientation on hammering: I. wrist motion and hammering performance. Human Factors 1989; 31(4): 397-411.
62 Masear VR, Hayes JM, Hyde AG. An industrial cause of carpal tunnel syndrome. The Journal of Hand Surgery 1986; 11A(2): 222-227.
63 McKenzie F, Storment J, Van Hook P, Armstrong TJ, A Program for Control of Repetitive Trauma Disorders Associated With Hand Tool Operations in a Telecommunications Manufacturing Facility, American Industrial Hygiene Association November 1985 46:11, 674-678.
64 Chatterjee, DS, Barwick DD, Petrie A, Exploratory electromyography in the study of vibration-induced white finger in the rock drillers. British Journal of Industrial Medicine 1981, 39: 89-97.
65 Wick W. Carpal tunnel syndrome: retailing: letters. Journal of Occupational Medicine 1981; 23(8): 524-525.
66 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
67 Bernard ML. Carpal tunnel syndrome: identification and control. Occupational Health Nursing 1979: 5-17.
68 Rothfleisch S, Sherman D. Carpal tunnel syndrome: biomechanical aspects of occupational occurrence and implications regarding surgical management. Orthopædic Review 1978; 7: 107-109.
69 Birbeck MQ, Beer TC. Occupation in relation to the carpal tunnel syndrome. Rheumatology and Rehabilitation 1975; 14: 218-221.
70 Hymovich L, Lindholm M. Hand, wrist and forearm injuries: the result of repetitive motions. Journal of Occupational Medicine 1966; 8(11): 573-577.
71 Phalen G.S. Spontaneous compression of the median nerve at the wrist. Journal of American Medical Association 1951; 45: 1128-1133.
72 Kremer M, Gilliatt RW, Golding JSR et al. Acroparæsthesiæ in the carpal-tunnel syndrome. Lancet 1953: 590-595.
73 Johnson BL, Testimony Before the Subcommitee on Postal Personnel and Modernization Committee on Post Office and Civil Service, U.S. House of Representatives, June 8, 1984.
74 Ibid
75 Crow RS. Treatment of the carpal-tunnel syndrome. British Medical Journal 1960: 1611-1615.
76 Hymovich L, Lindholm M. Hand, wrist and forearm injuries: the result of repetitive motions. Journal of Occupational Medicine 1966; 8(11): 573-577.
77 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
78 Rothfleisch S, Sherman D. Carpal tunnel syndrome: biomechanical aspects of occupational occurrence and implications regarding surgical management. Orthopædic Review 1978; 7: 107-109.
79 McKenzie F, Storment J, Van Hook P, Armstrong TJ, A Program for Control of Repetitive Trauma Disorders Associated With Hand Tool Operations in a Telecommunications Manufacturing Facility, American Industrial Hygiene Association November 1985 46:11, 674-678.
80 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
81 Bernard ML. Carpal tunnel syndrome: identification and control. Occupational Health Nursing 1979: 5-17.
82 McKenzie F, Storment J, Van Hook P, Armstrong TJ, A Program for Control of Repetitive Trauma Disorders Associated With Hand Tool Operations in a Telecommunications Manufacturing Facility, American Industrial Hygiene Association November 1985 46:11, 674-678.
83 Lipscomb PR. Tenosynovitis of the hand and the wrist: carpal tunnel syndrome, de Quervain's disease, trigger digit. Clinical Orthopedics 1958; 13: 164-181.
84 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
85 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
86 Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. Journal of Occupational Medicine 1981; 23(4): 255-258.
87 Louda L, Lukas L, Hygienic Aspects of Occupational Hand-Arm Vibration, Proceedings of the International Occupational Hand-Arm Vibration Conference, NIOSH, October 1975, Page 65.
88 Louda L, Lukas L, Hygienic Aspects of Occupational Hand-Arm Vibration, Proceedings of the International Occupational Hand-Arm Vibration Conference, NIOSH, October 1975, Page 65
89 NIOSH, Occupational Exposure to Hand-Arm Vibration, Criteria for a Recommended Standard. U.S. Government, Center for Disease Control, National Institute for Occupational Safety and Health, 1989.
90 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
91 Greenberg L, Chaffin D. Workers and Their Tools: A Guide to the Ergonomic Design of Hand Tools and Small Presses, Pendell Publishing, circa 1974. (The date of the publication is not included in the book. In a personal conversation with one of the authors (Chaffin) I was told that the book was published in about 1974.)
92 Tichauer ER. Some aspects of stress on forearm and hand in industry. Journal of Occupational Medicine 1966: 63-71.
93 Lipscomb PR. Tenosynovitis of the hand and the wrist: carpal tunnel syndrome, de Quervain's disease, trigger digit. Clinical Orthopedics 1958; 13: 164-181.
94 Brain RW, Wright DA, Wilkinson M. Spontaneous compression of both median nerves in the carpal tunnel. Lancet 1947: 277-282.
95 Wick W. Carpal tunnel syndrome: retailing: letters. Journal of Occupational Medicine 1981; 23(8): 524-525.
96 Tichauer ER, Gage H. Ergonomic principles basic to hand tool design. American Industrial Hygiene Association Journal 1977: 622-634.
97 The Industrial Environment-its Evaluation and Control. U.S. Government, Center for Disease Control, National Institute for Occupational Safety and Health. 1973.
98 Greenberg L, Chaffin D. Workers and Their Tools: A Guide to the Ergonomic Design of Hand Tools and Small Presses, Pendell Publishing, circa 1974. (The date of the publication is not included in the book. In a personal conversation with one of the authors (Chaffin) I was told that the book was published in about 1974.)
99 Tichauer ER, Sc.D. Ergonomics: the state of the art. American Industrial Hygiene Association Journal 1967: 105-116.
100 The Industrial Environment-its Evaluation and Control. U.S. Government, Center for Disease Control, National Institute for Occupational Safety and Health. 1973.
101 Bernard ML. Carpal tunnel syndrome: identification and control. Occupational Health Nursing 1979: 5-17.
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In addition to engineering controls, by 1979, other health professionals were implementing administrative controls, 101 such as pre-employment physicals with a detailed employee medical and occupational health history to help determine if any predisposing factors may exist. Where predisposing factors were identified, it was recommended that these employees be assigned job functions which did not place them at elevated risk.
References
1 Other synonyms for tendonitis include tenonitis; tenontitis; tenositis; tendosynovitis; tenosynovitis; tenontolemmitis; tenontothecitis; tendovaginitis; tenovaginitis; tendinitis. Although Steadman's and Dorlands's medical dictionaries give tenosynovitis and tenovaginitis as synonyms, some authors (Liscomb, 1958) maintain that when edema within the vagina occurs without stenosis, the condition is correctly termed "tenosynovitis"; and when the synovia are stenosing, the term "tenovaginitis" is correct.
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